<template>
  <ul class="list">
    <li 
      class="item" 
      v-for="item of letters" 
      :key="item"
      :ref="item"
      @touchstart="handleTouchStart"
      @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
      @click="handleLetterClick"
    >
      {{item}}
    </li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  computed: {
    letters(){
      const letters = []
       for (let i in this.cities) {
        letters.push(i)
       }
       return letters

    }
  },
  data () {
    return {
      touchStatus: false,
      startY:0,
      timer: null
    }
  },
  updated(){
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods:{
    handleLetterClick(e){
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart(){
      this.touchStatus = true
    },
    handleTouchMove(e){
      if(this.touchStatus){
        if(this.timer){
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(()=>{
          const touchY = e.touches[0].clientY - 129
          const index = Math.floor((touchY - this.startY)/22)
          if(index >= 0 && index < this.letters.length){
            this.$emit('change',this.letters[index])
          }
        }, 16)
        
      }
    },
    handleTouchEnd(){
      this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position:absolute
    top: 2.5rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .44rem
      text-align:  center
      color: $bgColor
</style>
